Thirty to forty percent of the things people say are focused on themselves. What’s more, 80% of posts on social media sites like Twitter and Facebook are also self-centered. To determine why, researchers at Harvard University performed brain scans on study participants to see how talking about oneself compared to other types of conversation. It turns out that sharing one’s own thoughts and feeling stimulates the same regions of the brain that are activated by food and sex.

In one exercise, participants were asked to either rate their own personality traits (to discuss how curious they are, for example) or those of famous people like Presidents George W. Bush or Barack Obama. Scans indicated that significantly more activity occurred in certain areas of the brain when people talked about themselves.

In another experiment, the researchers found that participants were even willing to forgo financial rewards for a chance to share their thoughts. The scientists noted that “participants valued sharing a response about the self at just under one cent…putting a new twist on the old phrase ‘a penny for your thoughts.'”

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